This application is based upon and claims the benefit of Japanese Patent Application No. 2002-30927 filed on Feb. 7, 2002, the contents of which are incorporated herein by reference.
The present invention relates to circuit boards with a lead frame that conducts current and radiates heat generated from an electronic component or components.
Conventionally, SMD (Surface Mount Device) mounting, i.e., surface mounting, is used for electrically connecting surface electronic components to a printed circuit board in order to increase the density of the surface electronic components on the printed circuit board. However, since SMD mounting is not good for radiating heat from the printed circuit board, it is necessary to attach a cooling fin to the printed circuit board when a power element from which a large quantity of heat is generated is mounted. Therefore, SMD mounting increases cost, and the size of the printed circuit board increases. Further, the SMD mounting requires connector terminals attached to the printed circuit board for electrically connecting external terminals (not shown) so that manufacturing processes thereof increase.
Lead frames are also utilized for mounting. FIG. 8 is a side view showing a lead frame circuit board J10 in which lead frames J11 are molded in resin J12. Lead type electronic components J20-J22 are typically mounted on the lead frame circuit board J10. However, in the lead frame circuit board J10, electrodes J11a on which the lead type electronic components J20-J22 are mounted are disposed inside of a surface of the lead frame circuit board J10. Accordingly, surface mount type electronic components cannot be mounted on the electrodes J11a. That is, an approximately flat surface is required for print solder paste so that solder paste cannot be printed on the surface of the lead frame circuit board J10 having the concave electrodes J11a. Further, small size surface mount type electronic components such as resistors, capacitors and transistors cannot also be mounted on the concave electrodes J11a because leads thereof do not extend outside and are typically too short to be bonded with the electrodes J11a. As a result, because electronic components cannot be concentrated on the lead frame circuit board, the lead frame circuit board cannot be miniaturized.
It is therefore an object of the present invention to provide a circuit board that is capable of obviating the above problems.
It is another object of the present invention to provide a circuit board that is capable of being miniaturized.
It is further object of the present invention to provide a circuit board that is capable of radiating heat.
According to a circuit board of the present invention, a lead frame includes an electrode for mounting an electronic component. A resin portion encapsulates the lead frame. The lead frame includes a step portion exposed from a surface of the resin portion so that the electrode is formed.
Accordingly, not only lead type electronic components but also the surface mount type electronic components can be mounted on the surface of the circuit board. Therefore, because the electronic components can be concentrated, the circuit board can be miniaturized.
According to another aspect of the present invention, the electrode is approximately coplanar with the surface of the resin portion. Therefore, solder paste or the like, which is used for electrically connecting the surface mount type electronic components to the electrode, can be printed on the surface of the circuit board.